Recently, an increasing number of metal machining techniques using a laser beam machine have been proposed. FIG. 4 schematically shows the arrangement of a conventional laser beam machine which is in wide use. In this laser beam machine, a laser beam 2 emitted from a laser oscillator 1 is reflected by mirrors 3 and 4 in a light guide passage 12 and introduced into a machining head 5. The laser beam is then focused by a parabolic mirror 6 and irradiated onto a surface of a workpiece 7. An auxiliary gas 10 is supplied from a gas cylinder, not shown, to a gas supply section 9 through a gas pipe 8. The auxiliary gas 10 is ejected from the gas supply section 9 and throttled by a nozzle 11 to be supplied to the workpiece 7. The surface of the workpiece 7 is melted due to interaction between the laser beam 2 and the auxiliary gas 10, whereby a laser beam machining is carried out.
In the laser beam machine shown in FIG. 4, however, a large amount of contaminants 13 such as spatters and oil mist (contaminative gas) is scattered from the workpiece 7 and enters the machining head 5. Such contaminants 13 stain the parabolic mirror 6 and even the light guide passage 12 and the mirrors 3 and 4. A problem therefore arises in that these parts must be frequently cleaned, making the maintenance difficult. Further, in the case of a three-dimensional machining operation using a laser beam machine so designed, the machining head 5 is oriented in every direction, sideways or upward, and thus can be even more contaminated by spatters and the like. Consequently, the application of three-dimensional laser beam machining is severely restricted.